量子点及量子点器件

量子点是纳米科学与技术研究重要的组成部分,量子点器件又是纳米器件的发展方向之一.详细介绍了量子点的分类、量子点的主要制备方式、量子点特性的传统研究和微波类比仿真研究方法,系统论述了量子点器件的分类应用及噪声抑制.     

HPT型Ge量子点红外探测器

异质结光敏晶体管(HPT)是一种具有内部电流增益的光电探测器,且与异质结双极晶体管(HBT)的制作工艺完全兼容.利用超高真空化学气相淀积(UHV/CVD)方法在HBT晶体管的基区和集电区间加入多层Ge量子点材料作为光吸收区.TEM和DCXRD测试结果表明,生长的多层Ge量子点材料具有良好的晶体质量.为了提高HPT的发射...     

A quantum dot image processor

A two-dimensional (2-D) periodic array of quantum dots, where each dot is coupled with its nearest neighbors and interfaced with an underlying material exhibiting a negative differential resistance, is theoretically investigated as a dynamical system for image processing. A circuit level study of such a system is performed and the circuit parameters for this paper are extracted by experimentally measuring them in an electrochemically self-assembled quasi-periodic quantum dot array. Large 2-D dot arrays with 4-neighborhood rectangular lattice structure are then simulated and it is shown that if image data are introduced as initial conditions to these arrays, the steady-state response of the system realizes an image processing task similar to edge detection-enhancement. In addition, the quantum dot architecture is capable of horizontal-vertical line detection with a simple arrangement of the coupling resistances between the dots. These applications are demonstrated via numerical experiments.     

Electrochemically self-assembled quantum dot arrays

We report some results pertaining to the magnetic, optical and topographic properties of electrochemically self-assembled quantum dots. Some of these dots self-order into two-dimensional hexagonal-close-packed arrays that are among the most periodic reported so far. We will review nonlinear optical properties of self-assembled CdS quantum dots and present new results pertaining to the nanomagnetic properties of cobalt dots. These structures may have important applications in magnetics, electronics and nonlinear optics.     

Colliding-pulse modelocked quantum dot lasers

Colliding pulse modelocking is demonstrated for the first time in quantum dot lasers. Using 3.9 mm-long devices with a 245 /spl mu/m-long central absorber, 7 ps pulses at a repetition rate of 20 GHz is obtained. For Gaussian pulses a time-bandwidth product close to the Fourier transform limit is determined. These results confirm the potential of quantum dot lasers for high repetition rate harmonic modelocking.     

半导体量子点量子光源研究进展

半导体量子点被认为是制备量子光源的最佳方案。量子点量子光源的可控性、纯度、亮度、全同性和相干性都有了很大的提高,已接近于应用水平。归纳了基于半导体量子点的量子光源研究进展中的关键问题,指出了半导体量子点量子光源在3个方面的主要进展,并讨论了关键制备技术,即半导体量子点作为单光子光源,实现了高全同性、高纯度、高收集效率等特性; 通过降低精细结构分裂效应等措施,量子点量子光源实现了具有高比特率、高保真度特性的光子纠缠; 量子点量子光源与平面电子线路和纳米光子系统的芯片集成取得了显著成效。在此基础上,对半导体量子点量子光源在量子信息领域的研究前景进行了展望。     

Relaxation oscillations of quantum dot lasers

The relaxation oscillation frequency of quantum dot lasers is modelled theoretically. Its dependency on the driving current, maximum gain, intersublevel relaxation time and homogeneous broadening is investigated. For suitable, feasible quantum dot laser parameters, relaxation oscillation frequencies up to 10 GHz are predicted. Making these devices useful for 5 Gbit/s communication systems     

Advances in self-assembled semiconductor quantum dot lasers

In the past 20 years the semiconductor laser has become a key device in optical electronics because of its pure output spectrum and high quantum efficiency. As the capabilities of laser diodes have grown, so has the range of applications contemplated for them. A great success in semiconductor lasers has been brought by the ability to artificially structure new materials on an atomic scale by using advanced crystal growth methods such as MBE and MOVPE. The laser performance successes gained using quantum wells in optoelectronic devices can be extended by adopting quantum wire and quantum dot structures. There have been several reports of successful lasing action in semiconductor dot structures within the past few years. In this article I will briefly review the recent progress in the development of quantum dot lasers.     

Inhomogeneous gain effects in quantum dot lasers

A comparison of optical and electrical derivative spectroscopy on a dual-state lasing InAs/GaAs quantum dot bilayer device is presented. The junction voltage cannot be described by a quasi-Fermi level separation and only partial clamping above the laser threshold was observed, demonstrating inhomogeneous gain. There is also competition between transverse optical modes which must be taken into account for a full understanding of dual-state lasing     

The quest for the quantum dot

Semiconductor devices that confine electrons within two-dimensional quantum wells are already in production. The zero-dimensional quantum dot promises super-efficient lasers with the last word in spectral purity. The author briefly discusses the definition of the electron and then goes on to discuss in more detail the quantum well obtained in the case of a GaAlAs-GaAs heterojunction. Further quantisation of the electron energy produces one dimensional quantum wires. By removing the one degree of freedom of the quantum wire leaves the quantum dot, zero degrees of freedom, the ultimate in energy quantisation     

PbS量子点同质P-N结光电探测器

PbS胶体量子点因其带隙可调、可溶液加工、吸收系数高等优异特性而广泛应用于光电探测器领域。然而基于光电二极管结构的PbS量子点光电探测器通常会使用不同的材料来制备N型层,从而增加了器件设计和工艺的复杂性,不利于这类光电探测器未来在面阵成像芯片中的应用。为简化制备工艺,提出了一种PbS量子点同质P-N结光电探测器,仅通过一种工艺过程实现了器件P型层和N型层的制备。经测试,探测器对不同入射光强度的探测表现出了良好的线性响应;在0.5 V反向偏压作用下,器件在700 nm处的响应度为0.11 A/W,比探测率为3.41×1011 Jones,展现出了其对弱光探测的优异能力。结果表明文中提出的PbS量子点同质PN结光电探测器有助于推动其在面阵成像领域中的发展。     

红外量子点材料的远距离识别

量子点分立的能级结构使其具有独特的光电性质,因而在激光能源、光电检测等领域应用广泛。其尺寸调谐的受激辐射特性与灵活多变的应用形态也使其成为一种理想的荧光标记材料,在生物医学、微观物质检测以及防伪与目标识别等领域备受关注。对于应用场景多为宏观自然环境的防伪与目标识别领域,不可避免地需要对红外波段的量子点荧光进行较远距离的检测与分析。因此,文中基于微弱信号检测技术设计构建了一套红外量子点荧光的远距离探测系统,并用其对PbS胶质量子点薄膜荧光进行了检测实验。实验结果及分析表明,波长~1300 nm的红外量子点荧光辐射可以在100~200 m距离之外被系统有效提取,从而实现红外量子点材料的远距离识别。系统对荧光特性的检测结果用于分析和指导不同红外量子点材料的制备过程,也将推动其远距离识别应用的多样性发展。     

抛物量子点中的二能级体系

采用Pekar类型的变分方法,在抛物量子点中电子与体纵光学声子（LO）强耦合的条件下,得出了电子的基态,第一激发态的能量及相应的波函数。讨论了电子-声子耦合强度,量子点受限长度对电子在基态∣0〉, 激发态∣1〉,叠加态时的概率密度分布的影响。结果显示叠加态时的概率密度随着电子-声子耦合强度的增加而增大,随着量子点受限长度的减小而增大。该结果对以量子点制备量子比特有重要的指导意义。     

Design of tunneling injection quantum dot lasers

In recent years, semiconductor quantum dot (QD) lasers have attracted considerable attention due to their potentia applications[1]. Although QD laser has been predicted can have more excellent performance than conventional quan- tum well laser, so far tem…     

Single electron transport in a free-standing quantum dot

We have fabricated a single quantum dot in the two-dimensional electron gas of a free-standing GaAs/AlGaAs heterostructure. Standard processing techniques are used to define the dot on a narrow mesa and selective etching undercuts the device to form a 120 nm thick free-standing beam connected to the substrate by source and drain regions. Work by Weig et al. [Phys. Rev. Lett. 92(4) (2004) 046804] on similar devices has provided evidence for phonon blockade which suppresses conduction at low temperatures and bias. Further studies are presented here that can only partially be explained by this theory. A similar gap in conductance has been seen, but evolution of the structure in a magnetic field suggests an alternative explanation of multiple dots in series, may better explain the results.     

柱形量子点的电子拉曼散射研究

本文对CdS柱形量子点的电子拉曼散射进行了研究;推导了拉曼散射截面的表达式,给出了有关的选择定则,获得了丰富的拉曼散射谱线并对谱线特点进行了分析和讨论,讨论结果直接给出了电子的有关信息。     

一种基于混合量子点的橙光量子点LED制备

为研究混合量子点(QD)发光二极管(QLED)的性能, 利用红、绿量子点混合作为发光层,制备了结构为 ITO/PEDOT:PSS/poly-TPD/QDs(红、绿1∶1混合)/ZnO/Al的橙光QLED,并与 结构为 ITO/PEDOT:PSS/poly-TPD/QDs(红光)/ZnO/Al的红光QLED进行了对比。实验结果表明, 基于红、绿QD混合的橙光QLED的制备方法是有效的,制备的橙光QLED 电流密度和亮度均小 于红光QLED, 但电流效率远大于红光QLED。研究发现,器件性能与各功能层能级以及厚度密切相关,应通 过选取适当能 级的发光层材料,将注入的空穴以及电子同时限制在发光层内从而提高器件的电流效率,并 调节各功能层 厚度使得载流子注入平衡从而提高器件性能。     

Analysis of spatial modes in half-disk lasers based on AlGaAsSb/InGaAsSb quantum well nanoheterostructures

Spectral and spatial distributions of the emission of whispering-gallery-mode (WGM) lasers with a half-disk cavity have been studied. Up to 13 broad lobes with different intensities, subdivided into order-of-magnitude narrower lobes, are distinguished in the spatial distribution. The emission spectrum is nearly single-mode. A mathematical model of the electromagnetic field distribution in a WGM laser is suggested, and the radiation pattern of the laser is calculated. It is shown that each lobe corresponds to its own stable radial spatial mode. The highest emission intensity is provided not by the peripheral mode itself, but by the next-closest mode, which presumably exhibits the lowest optical loss. The predominance of a single spatial mode results in a nearly single-mode emission spectrum being observed.     

InGaAs/GaAs量子点红外探测器

与量子阱红外探测器相比,量子点红外探测器具有不制作表面光栅就能在垂直入射红外光照射下工作以及工作温度更高等优势。然而,目前阻碍量子点红外探测器性能提高的技术瓶颈主要来自组装量子点较差的大小均匀性、较低的量子点密度以及垂直入射下子带跃迁吸收效率低等原因。利用分子束外延技术研究了如何从量子点材料生长和器件设计两方面来克服这些困难,并且制作了几种不同结构的InGaAs/GaAs量子点红外探测器。 在77 K时,这些器件在垂直入射条件下观察到了很强的光电流信号。